Macrophages Of Wild-type Mice Research Articles

Cardiomyocyte NOX4 regulates resident macrophage-mediated inflammation and diastolic dysfunction in stress cardiomyopathy

In acute sympathetic stress, catecholamine overload can lead to stress cardiomyopathy. We tested the hypothesis that cardiomyocyte NOX4 (NADPH oxidase 4)-dependent mitochondrial oxidative stress mediates inflammation and diastolic dysfunction in stress cardiomyopathy. Isoproterenol (ISO; 5 mg/kg) injection induced sympathetic stress in wild-type and cardiomyocyte (CM)-specific Nox4 knockout (Nox4CM−/−) mice. Wild-type mice treated with ISO showed higher CM NOX4 expression, H2O2 levels, inflammasome activation, and IL18, IL6, CCL2, and TNFα levels than Nox4CM−/− mice. Spectral flow cytometry and t-SNE analysis of cardiac cell suspensions showed significant increases in pro-inflammatory and pro-fibrotic embryonic-derived resident (CCR2−MHCIIhiCX3CR1hi) macrophages in wild-type mice 3 days after ISO treatment, whereas Nox4CM−/− mice had a higher proportion of embryonic-derived resident tissue-repair (CCR2−MHCIIloCX3CR1lo) macrophages. A significant increase in cardiac fibroblast activation and interstitial collagen deposition and a restrictive pattern of diastolic dysfunction with increased filling pressure was observed in wild-type hearts compared with Nox4CM−/− 7 days post-ISO. A selective NOX4 inhibitor, GKT137831, reduced myocardial mitochondrial ROS, macrophage infiltration, and fibrosis in ISO-injected wild-type mice, and preserved diastolic function. Our data suggest sympathetic overstimulation induces resident macrophage (CCR2−MHCII+) activation and myocardial inflammation, resulting in fibrosis and impaired diastolic function mediated by CM NOX4-dependent ROS.

The Triterpenoid CDDO-Methyl Ester Redirects Macrophage Polarization and Reduces Lung Tumor Burden in a Nrf2-Dependent Manner.

The NRF2/KEAP1 pathway protects healthy cells from malignant transformation and maintains cellular homeostasis. Up to 30% of human lung tumors gain constitutive NRF2 activity which contributes to cancer cell survival and chemoresistance, but the effects of NRF2 activation in immune cells within the tumor microenvironment are underexplored. Macrophages can promote cancer progression or regression depending on context, and NRF2 activation affects macrophage activity. The NRF2 activator CDDO-Methyl ester (CDDO-Me or bardoxolone methyl) reprogrammed Nrf2 wild-type (WT) tumor-educated bone marrow-derived macrophages (TE-BMDMs) from a tumor-promoting to a tumor-inhibiting phenotype, marked by an increase in M1 markers TNFα, IL-6, and MHC-II and a decrease in the tumor-promoting factors VEGF, CCL2, and CD206. No changes were observed in Nrf2 knockout (KO) TE-BMDMs. CDDO-Me decreased tumor burden (p < 0.001) and improved pathological grade (p < 0.05) in WT but not Nrf2 KO A/J mice. Tumor burden in Nrf2 KO mice was 4.6-fold higher (p < 0.001) than in WT mice, irrespective of treatment. CDDO-Me increased the number of lung-infiltrating macrophages in WT mice but lowered CD206 expression in these cells (p < 0.0001). In summary, Nrf2 KO exacerbates lung tumorigenesis in A/J mice, and CDDO-Me promotes an Nrf2-dependent, anti-cancer macrophage phenotype.

Targeting the Macrophage: Immune Cells May Be the Key to Phthalate-Induced Liver Toxicity.

Targeting the Macrophage: Immune Cells May Be the Key to Phthalate-Induced Liver Toxicity.

Histidine decarboxylase deficiency inhibits NBP-induced extramedullary hematopoiesis by modifying bone marrow and spleen microenvironments.

Histidine decarboxylase (HDC), a histamine synthase, is expressed in various hematopoietic cells and is induced by hematopoietic cytokines such as granulocyte colony-stimulating factor (G-CSF). We previously showed that nitrogen-containing bisphosphonate (NBP)-treatment induces extramedullary hematopoiesis via G-CSF stimulation. However, the function of HDC in NBP-induced medullary and extramedullary hematopoiesis remains unclear. Here, we investigated changes in hematopoiesis in wild-type and HDC-deficient (HDC-KO) mice. NBP treatment did not induce anemia in wild-type or HDC-KO mice, but did produce a gradual increase in serum G-CSF levels in wild-type mice. NBP treatment also enhanced Hdc mRNA expression and erythropoiesis in the spleen and reduced erythropoiesis in bone marrow and the number of vascular adhesion molecule 1 (VCAM-1)-positive macrophages in wild-type mice, as well as increased the levels of hematopoietic progenitor cells and proliferating cells in the spleen and enhanced expression of bone morphogenetic protein 4 (Bmp4), CXC chemokine ligand 12 (Cxcl12), and hypoxia inducible factor 1 (Hif1) in the spleen. However, such changes were not observed in HDC-KO mice. These results suggest that histamine may affect hematopoietic microenvironments of the bone marrow and spleen by changing hematopoiesis-related factors in NBP-induced extramedullary hematopoiesis.

CX3CR1 Deficiency Attenuates DNFB-Induced Contact Hypersensitivity Through Skewed Polarization Towards M2 Phenotype in Macrophages.

CX3CL1 can function as both an adhesion molecule and a chemokine for CX3CR1+ cells, such as T cells, monocytes, and NK cells. Recent studies have demonstrated that CX3CL1–CX3CR1 interaction is associated with the development of various inflammatory skin diseases. In this study, we examined CX3CR1 involvement in 2,4-dinitrofluorobenzene (DNFB)-induced contact hypersensitivity using CX3CR1−/− mice. Ear swelling and dermal edema were attenuated after DNFB challenge in CX3CR1−/− mice. Expression of TNF-α, IL-6, and M1 macrophage markers was decreased in the ears of CX3CR1−/− mice, whereas expression of M2 macrophage markers including arginase-1 was increased. Decreased TNF-α and IL-6 expression and increased arginase-1 expression were found in peritoneal macrophages from CX3CR1−/− mice. Furthermore, ear swelling was attenuated by depleting dermal macrophages in wild-type mice to a similar level to CX3CR1−/− mice. These results suggest that CX3CR1 deficiency could induce skewed polarization towards M2 phenotype in macrophages, resulting in attenuation of contact hypersensitivity response.

Targeted knock-in mice expressing the oxidase-fixed form of xanthine oxidoreductase favor tumor growth

Xanthine oxidoreductase has been implicated in cancer. Nonetheless, the role played by its two convertible forms, xanthine dehydrogenase (XDH) and oxidase (XO) during tumorigenesis is not understood. Here we produce XDH-stable and XO-locked knock-in (ki) mice to address this question. After tumor transfer, XO ki mice show strongly increased tumor growth compared to wild type (WT) and XDH ki mice. Hematopoietic XO expression is responsible for this effect. After macrophage depletion, tumor growth is reduced. Adoptive transfer of XO-ki macrophages in WT mice increases tumor growth. In vitro, XO ki macrophages produce higher levels of reactive oxygen species (ROS) responsible for the increased Tregs observed in the tumors. Blocking ROS in vivo slows down tumor growth. Collectively, these results indicate that the balance of XO/XDH plays an important role in immune surveillance of tumor development. Strategies that inhibit the XO form specifically may be valuable in controlling cancer growth.

Therapeutic ultrasound attenuates DSS-induced colitis through the cholinergic anti-inflammatory pathway.

BackgroundUlcerative Colitis (UC) is an Inflammatory Bowel Disease (IBD) characterized by uncontrolled immune response, diarrhoea, weight loss and bloody stools, where sustained remission is not currently achievable. Dextran Sulphate Sodium (DSS)-induced colitis is an animal model that closely mimics human UC. Ultrasound (US) has been shown to prevent experimental acute kidney injury through vagus nerve (VN) stimulation and activation of the cholinergic anti-inflammatory pathway (CAIP). Since IBD patients may present dysfunctional VN activity, our aim was to determine the effects of therapeutic ultrasound (TUS) in DSS-induced colitis.MethodsAcute colitis was induced by 2% DSS in drinking water for 7 days and TUS was administered to the abdominal area for 7 min/day from days 4–10. Clinical symptoms were analysed, and biological samples were collected for proteomics, macroscopic and microscopic analysis, flow cytometry and immunohistochemistry.FindingsTUS attenuated colitis by reducing clinical scores, colon shortening and histological damage, inducing proteomic tolerogenic response in the gut during the injury phase and early recovery of experimental colitis. TUS did not improve clinical and pathological outcomes in splenectomised mice, while α7nAChR (α7 nicotinic acetylcholine receptor - indicator of CAIP involvement) knockout animals presented with disease worsening. Increased levels of colonic F4/80+α7nAChR+ macrophages in wild type mice suggest CAIP activation.InterpretationThese results indicate TUS improved DSS-induced colitis through stimulation of the splenic nerve along with possible contribution by VN with CAIP activation.FundIntramural Research Programs of the Clinical Centre, the National Institute of Biomedical Imaging and Bioengineering at the NIH and CAPES/Brazil.

CD24 regulates Ly6Chi macrophages and BDL-induced liver fibrosis

Objective To investigate the regulatory effects of CD24 on Ly6Chi macrophages in liver and its influences on bile duct ligation (BDL)-induced hepatic fibrosis in mice. Methods Liver fibrosis was induced in wild-type (WT) and CD24-/- mice by surgical ligation of the biliary duct. Levels of alanine amino transferase (ALT) in serum were detected and liver sections were stained with haematoxylin and eosin (H&E) staining to assess the severity of liver injury. Sirius Red staining was used to observe the degree of liver fibrosis. Real-time PCR was performed for detecting the expression of hepatic fibrosis-related markers and TGF-β1 at mRNA level. The percentage of macrophages and the number of TGF-β1-producing macrophages were measured by flow cytometry. Results BDL-induced liver fibrosis was exacerbated in CD24-/- mice than in WT mice as demonstrated by more serious hyperplasia in bile duct, more inflammatory infiltration at the portal area and higher levels of ALT in serum. Results of Sirius red staining also showed that the liver fibrosis was more severe in CD24-/- mice than in WT mice. Moreover, α-SMA and collagen typeⅠ alpha 1 (Col1a1) were significantly upregulated in CD24-/- mice. Flow cytometry analysis revealed that CD24 was highly expressed by hepatic macrophages in BDL-induced WT mice, and the percentages of hepatic macrophages were significantly elevated in CD24-/- mice compared with those in WT mice. Further analysis revealed that the percentages of Ly6Chi hepatic macrophages in CD24-/- mice were higher than those in WT mice, but there was no significant difference in the percentages of Ly6Clo macrophages. The expression of TGF-β1 at mRNA level was increased in CD24-/- mice as compared with that in WT mice after BDL. Moreover, intracellular staining showed that Ly6Chi hepatic macrophages in CD24-/- mice secreted more TGF-β1 than the macrophages in WT mice. Conclusions CD24 might attenuate the BDL-induced liver fibrosis in mice via regulating the percentage of hepatic Ly6Chi macrophages and the secretion of TGF-β1. Key words: CD24; Bile duct ligation (BDL); Liver fibrosis; Ly6Chi hepatic macrophage; TGF-β1

Trichomonas vaginalis Induces Production of Proinflammatory Cytokines in Mouse Macrophages Through Activation of MAPK and NF-κB Pathways Partially Mediated by TLR2.

Trichomoniasis, caused by Trichomonas vaginalis infection, is the most prevalent sexually transmitted disease in female and male globally. However, the mechanisms by innate immunity against T. vaginalis infection have not been fully elucidated. Toll-like receptor2 (TLR2) has been shown to be involved in pathogen recognition, innate immunity activation, and inflammatory response to the pathogens. Nonetheless, the function of TLR2 against T. vaginalis remains unclear. In the present study, we investigated the role of TLR2 in mouse macrophages against T. vaginalis. RT-qPCR analysis revealed that T. vaginalis stimulation increased the gene expression of TLR2 in wild-type (WT) mouse macrophages. T. vaginalis also induced the secretion of IL-6, TNF-α, and IFN-γ in WT mouse macrophages, and the expression of these cytokines significantly decreased in TLR2-/- mouse macrophages and in WT mouse macrophages pretreated with MAPK inhibitors SB203580 (p38) and PD98059 (ERK). Western blot analysis demonstrated that T. vaginalis stimulation induced the activation of p38, ERK, and p65 NF-κB signal pathways in WT mouse macrophages, and the phosphorylation of p38, ERK, and p65 NF-κB significantly decreased in TLR2-/- mouse macrophages. Taken together, our data suggested that T. vaginalis may regulates proinflammatory cytokines production by activation of p38, ERK, and NF-κB p65 signal pathways via TLR2 in mouse macrophages. TLR2 might be involved in the defense and elimination of T. vaginalis infection.

Expansion of EPOR-negative macrophages besides erythroblasts by elevated EPOR signaling in erythrocytosis mouse models.

Activated erythropoietin (EPO) receptor (EPOR) signaling causes erythrocytosis. The important role of macrophages for the erythroid expansion and differentiation process has been reported, both in baseline and stress erythropoiesis. However, the significance of EPOR signaling for regulation of macrophages contributing to erythropoiesis has not been fully understood. Here we show that EPOR signaling activation quickly expands both erythrocytes and macrophages in vivo in mouse models of primary and secondary erythrocytosis. To mimic the chimeric condition and expansion of the disease clone in the polycythemia vera patients, we combined Cre-inducible Jak2V617F/+ allele with LysM-Cre allele which expresses in mature myeloid cells and some of the HSC/Ps (LysM-Cre;Jak2V617F/+ mice). We also generated inducible EPO-mediated secondary erythrocytosis models using Alb-Cre, Rosa26-loxP-stop-loxP-rtTA, and doxycycline inducible EPAS1-double point mutant (DPM) alleles (Alb-Cre;DPM mice). Both models developed a similar degree of erythrocytosis. Macrophages were also increased in both models without increase of major inflammatory cytokines and chemokines. EPO administration also quickly induced these macrophages in wild-type mice before observable erythrocytosis. These findings suggest that EPOR signaling activation could induce not only erythroid cell expansion, but also macrophages. Surprisingly, an in vivo genetic approach indicated that most of those macrophages do not express EPOR, but erythroid cells and macrophages contacted tightly with each other. Given the importance of the central macrophages as a niche for erythropoiesis, further elucidation of the EPOR signaling mediated-regulatory mechanisms underlying macrophage induction might reveal a potential therapeutic target for erythrocytosis.

TLR2−/− Mice Display Decreased Severity of Giardiasis via Enhanced Proinflammatory Cytokines Production Dependent on AKT Signal Pathway

Giardia infection is one of the most common causes of waterborne diarrheal disease in a wide array of mammalian hosts, including humans globally. Although numerous studies have indicated that adaptive immune responses are important for Giardia defense, however, whether the host innate immune system such as TLRs recognizes Giardia remains poorly understood. TLR2 plays a crucial role in pathogen recognition, innate immunity activation, and the eventual pathogen elimination. In this study, we investigated the role of TLR2 as a non-protective inflammatory response on controlling the severity of giardiasis. RT-PCR analysis suggested that TLR2 expression was increased in vitro. We demonstrated that Giardia lamblia-induced cytokines expression by the activation of p38 and ERK pathways via TLR2. Interestingly, the expression of IL-12 p40, TNF-α, and IL-6, but not IFN-γ, was enhanced in TLR2-blocked and TLR2−/− mouse macrophages exposed to G. lamblia trophozoites compared with wild-type (WT) mouse macrophages. Further analysis demonstrated that G. lamblia trophozoites reduced cytokines secretion by activating AKT pathway in WT mouse macrophages. Immunohistochemical staining in G. lamblia cysts infected TLR2−/− and WT mice showed that TLR2 was highly expressed in duodenum in infected WT mice. Also, infected TLR2−/− and AKT-blocked mice showed an increased production of IL-12 p40 and IFN-γ compared with infected WT mice at the early stage during infection. Interestingly, infected TLR2−/− and AKT-blocked mice displayed a decreased parasite burden, an increased weight gain rate, and short parasite persistence. Histological morphometry showed shortened villus length, hyperplastic crypt and decreased ratio of villus height/crypt depth in infected WT mice compared with in infected TLR2−/− and AKT-blocked mice. Together, our results suggested that TLR2 deficiency leads to alleviation of giardiasis and reduction of parasite burden through the promotion of proinflammatory cytokines production. For the first time, our results demonstrated that TLR2 played a negative role in host defense against Giardia.

Prostaglandin E2 blockade enhances the pulmonary anti-Cryptococcus neoformans immune reaction via the induction of TLR-4

The present study aimed to explore whether the inhibition of prostaglandin E2 enhances pulmonary anti-Cryptococcus neoformans immunity. Lung colony forming unit (CFU) assays demonstrated that the cryptococcal infection was dramatically depressed in mice given EP2 and EP4 or single EP antagonist treatment compared to the untreated wild type mice (p<0.05), leading to the increased survival of the infected mice by 8-9 days or 2-4 days, respectively. RT-PCR and flow cytometry assays showed that the expression of IFN-γ, IL-17, IL-22 in M1 macrophages and IL-10 in M2 macrophages increased significantly at 1week post-infection in mice with either EP2 or EP4 blockade (p<0.05). The polarization of alveolar macrophages showed that, at 1week post infection, the alveolar macrophages in untreated wild type mice, TLR4-/- mice and TLR4-/- mice with EP2 and EP4 blockade were strongly M2 polarized, whereas the alveolar macrophages in wild type mice with EP2 and EP4 blockade were M1 polarized. In conclusion, the blockade of EP2 and EP4 promotes mouse survival after cryptococcus infection by promoting the production of cytokines via TLR4, as well as the enhanced M1 polarization of alveolar macrophages.

Abstract 534: Abca1 Mediates Macrophage Deposition of Cholesterol Into the Extracellular Matrix

ABCG1 and ABCA1 both function in reverse cholesterol transport. We previously reported that cholesterol-enriched macrophages deposit cholesterol into the extracellular space and this process depends in part on ABCG1. The extracellular cholesterol deposits can be mobilized by HDL. The objective of the current study was to determine whether ABCA1 also contributes to macrophage deposition of extracellular cholesterol. A monoclonal antibody that detects cholesterol microdomains, and not isolated cholesterol molecules, labels these extracellular deposits. First, to confirm the specificity of the cholesterol labeling, we treated cholesterol-enriched macrophages cultures with cholesterol oxidase and found that antibody labeling of deposits was eliminated. Many biochemical studies assume that cholesterol oxidase susceptible cholesterol indicates this cholesterol is within the plasma membrane. However, as we show here, the extracellular pool of cholesterol also contributes to cholesterol oxidase susceptible cholesterol. Second, concerning ABCA1 function in cholesterol deposition, we observed that the LXR agonist, TO901317, an ABCA1-inducing agent, restored cholesterol deposition that was absent in ABCG1-/- mouse macrophages. In addition, probucol, an agent that inhibits ABCA1 function, partially inhibited cholesterol deposited by wild-type mouse macrophages, and completely inhibited deposition from TO901317-treated ABCG1-/- mouse macrophages. These results suggest that ABCA1 contributes to macrophage cholesterol deposition. We confirmed this conclusion by testing cholesterol deposition in ABCA1-/- mouse macrophages. Extracellular cholesterol deposition by these macrophages was substantially reduced compared with wild-type mouse macrophages. Thus, our findings demonstrate a novel function of ABCA1 in contributing to macrophage export of cholesterol into the extracellular space where this cholesterol can be stored until mobilized by HDL.

Deriving a cardiac ageing signature to reveal MMP-9-dependent inflammatory signalling in senescence.

Cardiac ageing involves the progressive development of cardiac fibrosis and diastolic dysfunction coordinated by MMP-9. Here, we report a cardiac ageing signature that encompasses macrophage pro-inflammatory signalling in the left ventricle (LV) and distinguishes biological from chronological ageing. Young (6-9 months), middle-aged (12-15 months), old (18-24 months), and senescent (26-34 months) mice of both C57BL/6J wild type (WT) and MMP-9 null were evaluated. Using an identified inflammatory pattern, we were able to define individual mice based on their biological, rather than chronological, age. Bcl6, Ccl24, and Il4 were the strongest inflammatory markers of the cardiac ageing signature. The decline in early-to-late LV filling ratio was most strongly predicted by Bcl6, Il1r1, Ccl24, Crp, and Cxcl13 patterns, whereas LV wall thickness was most predicted by Abcf1, Tollip, Scye1, and Mif patterns. With age, there was a linear increase in cardiac M1 macrophages and a decrease in cardiac M2 macrophages in WT mice; of which, both were prevented by MMP-9 deletion. In vitro, MMP-9 directly activated young macrophage polarization to an M1/M2 mid-transition state. Our results define the cardiac ageing inflammatory signature and assign MMP-9 roles in mediating the inflammaging profile by indirectly and directly modifying macrophage polarization. Our results explain early mechanisms that stimulate ageing-induced cardiac fibrosis and diastolic dysfunction.

Regulatory function of interferon regulatory factor 3 in obesity, inflammation and insulin resistance (HUM7P.287)

Abstract Obesity is a major risk factor for diseases ranging from insulin resistance, type 2 diabetes mellitus to nonalcoholic fatty liver disease. Obesity is associated with a state of chronic, low-grade inflammation. In this study, we found the important regulatory role of interferon regulatory factor 3 (IRF3), a master regulator of type I interferon-dependent immune responses, in obesity. We found that the expression of IRF3 was increased in white adipose tissue (WAT) from mice fed with high fat diet compared with that from mice fed with normal chow. IRF3 knockout (KO) mice developed obesity spontaneously with increased adiposity compared with wild-type (WT) controls. Deficiency of IRF3 in mice resulted in impaired insulin sensitivity and lipid homeostasis. The development of obesity in IRF3 KO mice was associated with increased infiltration of macrophages which was more inflammatory in the WAT compared with macrophages in WT mice. IRF3 deficient macrophages exhibited increased M1 polarization than WT cells. Additionally, IRF3 KO mice developed hepatic steatosis with increased expression of lipogenesis genes in the liver. Our study therefore demonstrated that IRF3 played an important role in the regulation of insulin sensitivity, inflammation and lipid homeostasis, which may provide a new strategy for treatment of obesity, type 2 diabetes mellitus and hepatic steatosis.

The role of monocyte subsets in myocutaneous revascularization

BackgroundThe controlled recruitment of monocytes from the circulation to the site of injury and their differentiation into tissue macrophages are critical events in the reconstitution of tissue integrity. Subsets of monocytes/macrophages have been implicated in the pathogenesis of atherosclerosis and tumor vascularity; however, the significance of monocyte heterogeneity in physiologic neovascularization is just emerging. Materials and methodsA cranial-based, peninsular-shaped myocutaneous flap was surgically created on the dorsum of wild-type mice (C57BL6) and populations of mice with genetic deletion of subset-specific chemokine ligand-receptor axes important in monocyte trafficking and function (CCL2−/− and CX3CR1−/−) (n=36 total; 12 mice per group, nine with flap and three unoperated controls). Planimetric analysis of digital photographic images was utilized to determine flap surface viability in wild-type and knockout mice. Real-time myocutaneous flap perfusion and functional revascularization was determined by laser speckle contrast imaging. Image analysis of CD-31 immunostained sections confirmed flap microvascular density and anatomy. Macrophage quantification and localization in flap tissues was determined by F4/80 gene and protein expression. Quantitative reverse transcription-polymerase chain reaction was performed on nonoperative back skin and postoperative flap tissue specimens to determine local gene expression. ResultsMyocutaneous flaps created on wild type and CX3CR1−/− mice were engrafted to the recipient site, resulting in viability. In contrast, distal full thickness cutaneous necrosis and resultant flap dehiscence was evident by d 10 in CCL2−/− mice. Over 10 d, laser speckle contrast imaging documented immediate graded flap ischemia in all three groups of mice, functional flap revascularization in wild type and CX3CR1−/− mice, and lack of distal flap reperfusion in CCL2−/− mice. Immunostaining of serial histologic specimens confirmed marked increases in microvascular density and number of macrophages in wild type mice, intermediate increases in CX3CR1−/− mice, and no significant change in vessel count or macrophage quantity in CCL2−/− mice over the study interval. Finally, quantitative reverse transcriptase polymerase chain reaction demonstrated that the loss of function of chemokine ligand and receptor genes influenced the transcription of local genes involved in monocyte chemotaxis and wound angiogenesis. ConclusionsIn a graded-ischemia wound healing model, monocyte recruitment was severely impaired in CCL2−/− mice, resulting in failure of flap revascularization and concomitant cutaneous necrosis. Analysis of CX3CR1-deficient mice revealed adequate monocyte recruitment and revascularization for flap survival; however, the myeloid cell response and magnitude of neovascularization were dampened compared with wild type mice.

Role of Mincle in Alveolar Macrophage-Dependent Innate Immunity against Mycobacterial Infections in Mice

The role of macrophage-inducible C-type lectin Mincle in lung innate immunity against mycobacterial infection is incompletely defined. In this study, we show that wild-type (WT) mice responded with a delayed Mincle induction on resident alveolar macrophages and newly immigrating exudate macrophages to infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG), peaking by days 14-21 posttreatment. As compared with WT mice, Mincle knockout (KO) mice exhibited decreased proinflammatory mediator responses and leukocyte recruitment upon M. bovis BCG challenge, and they demonstrated increased mycobacterial loads in pulmonary and extrapulmonary organ systems. Secondary mycobacterial infection on day 14 after primary BCG challenge led to increased cytokine gene expression in sorted alveolar macrophages of WT mice, but not Mincle KO mice, resulting in substantially reduced alveolar neutrophil recruitment and increased mycobacterial loads in the lungs of Mincle KO mice. Collectively, these data show that WT mice respond with a relatively late Mincle expression on lung sentinel cells to M. bovis BCG infection. Moreover, M. bovis BCG-induced upregulation of C-type lectin Mincle on professional phagocytes critically shapes antimycobacterial responses in both pulmonary and extrapulmonary organ systems of mice, which may be important for elucidating the role of Mincle in the control of mycobacterial dissemination in mice.

A Caspase for Phagosomal-Lysosomal Fusion

Clearance of phagosomes containing pathogenic bacteria depends on caspase-11.

Prostaglandin E2 restrains macrophage maturation via E prostanoid receptor 2/protein kinase A signaling

AbstractProstaglandin E2 (PGE2) is a lipid mediator that acts by ligating 4 distinct G protein–coupled receptors, E prostanoid (EP) 1 to 4. Previous studies identified the importance of PGE2 in regulating macrophage functions, but little is known about its effect on macrophage maturation. Macrophage maturation was studied in vitro in bone marrow cell cultures, and in vivo in a model of peritonitis. EP2 was the most abundant PGE2 receptor expressed by bone marrow cells, and its expression further increased during macrophage maturation. EP2-deficient (EP2−/−) macrophages exhibited enhanced in vitro maturation compared with wild-type cells, as evidenced by higher F4/80 expression. An EP2 antagonist also increased maturation. In the peritonitis model, EP2−/− mice exhibited a higher percentage of F4/80high/CD11bhigh cells and greater expression of macrophage colony-stimulating factor receptor (M-CSFR) in both the blood and the peritoneal cavity. Subcutaneous injection of the PGE2 analog misoprostol decreased M-CSFR expression in bone marrow cells and reduced the number of peritoneal macrophages in wild-type mice but not EP2−/− mice. The suppressive effect of EP2 ligation on in vitro macrophage maturation was mimicked by a selective protein kinase A agonist. Our findings reveal a novel role for PGE2/EP2/protein kinase A signaling in the suppression of macrophage maturation.

Acyl-CoA synthetase 1 is required for oleate and linoleate mediated inhibition of cholesterol efflux through ATP-binding cassette transporter A1 in macrophages

Diabetes and insulin resistance increase the risk of cardiovascular disease caused by atherosclerosis through mechanisms that are poorly understood. Lipid-loaded macrophages are key contributors to all stages of atherosclerosis. We have recently shown that diabetes associated with increased plasma lipids reduces cholesterol efflux and levels of the reverse cholesterol transporter ABCA1 (ATP-binding cassette transporter A1) in mouse macrophages, which likely contributes to macrophage lipid accumulation in diabetes. Furthermore, we and others have shown that unsaturated fatty acids reduce ABCA1-mediated cholesterol efflux, and that this effect is mediated by the acyl-CoA derivatives of the fatty acids. We therefore investigated whether acyl-CoA synthetase 1 (ACSL1), a key enzyme mediating acyl-CoA synthesis in macrophages, could directly influence ABCA1 levels and cholesterol efflux in these cells. Mouse macrophages deficient in ACSL1 exhibited reduced sensitivity to oleate- and linoleate-mediated ABCA1 degradation, which resulted in increased ABCA1 levels and increased apolipoprotein A-I-dependent cholesterol efflux in the presence of these fatty acids, as compared with wildtype mouse macrophages. Conversely, overexpression of ACSL1 resulted in reduced ABCA1 levels and reduced cholesterol efflux in the presence of unsaturated fatty acids. Thus, the reduced ABCA1 and cholesterol efflux in macrophages subjected to conditions of diabetes and elevated fatty load may, at least in part, be mediated by ACSL1. These observations raise the possibility that ABCA1 levels could be increased by inhibition of acyl-CoA synthetase activity in vivo. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945–2010).